Dissociation kinetics aquatic complexes

Activation volumes for aquation of Schiff base complexes [Fe(C5H4NCH=NHR)3]2+ (R = Me, Et, nPr, nBu) are between +11 and +14 cm3 mol-1 (107), and thus within the range established earlier (108) for (substituted) tris-l,10-phenanthroline-iron(II) complexes, viz. +11 to +22 cm3 mol-1. These positive values are consistent with dissociative activation. Kinetic studies of the reaction of a CH2S(CH2)3SCH2 -linked bis(terpy) ligand (L6) with [Fe(terpy)2]2+ showed a very slow two-step process. The suggested mechanism consisted of slow loss of one terpy, rapid formation of [Fe(terpy)(L6)], and finally slow displacement of the second terpy as the partially-bonded L6 becomes hexadentate (109). 

Acid-promoted aquation of the binuclear complex Cu2L of the hexaaza macrocycle L = 2,5,8,17,20,23 -hexaaza[9.9]paracyclophane, whose half-life is of the order of a second, exhibits simple one-stage first-order kinetics. This is attributed to parallel reactions at each Cu(II) center having identical rate constants (305). The kinetics of dissociation of mono- and... 

The dependence of rate constants for approach to equilibrium for reaction of the mixed oxide-sulfide complex [Mo3((i3-S)((i-0)3(H20)9] 1+ with thiocyanate has been analyzed into formation and aquation contributions. These reactions involve positions trans to p-oxo groups, mechanisms are dissociative (391). Kinetic and thermodynamic studies on reaction of [Mo3MS4(H20)io]4+ (M = Ni, Pd) with CO have yielded rate constants for reaction with CO. These were put into context with substitution by halide and thiocyanate for the nickel-containing cluster (392). A review of the chemistry of [Mo3S4(H20)9]4+ and related clusters contains some information on substitution in mixed metal derivatives [Mo3MS4(H20)re]4+ (M = Cr, Fe, Ni, Cu, Pd) (393). There are a few asides of mechanistic relevance in a review of synthetic Mo-Fe-S clusters and their relevance to nitrogenase (394). 

The preparation and characterization of K3[0s(CN)5(NH3)] 2H20 have been described. This complex is a useful starting material for the synthesis of other [Os (CN)5L] species (e.g., L = py, pyz) and [0s(CN)5(H20)] can be obtained by the controlled aquation of [Os(Cf 5(NH3)f The kinetics of these ligand displacements have been investigated and mechanisms for the processes have been discussed. The UV-vis spectrum of each complex in the series [Os"(CN)5L] in which L is py, pyz, Mepz, or derivatives thereof, exhibits an intense, asymmetric MLCT absorption, split by spin-orbit coupling, and the effects of the electronic properties of L on the spectra have been examined. Redox properties of the complexes and the kinetics of the dissociation of pyz from [Os(CN)s(pyz)] have also been reported. ... 

Basic hydrolysis of [Ru(NH3)jX]X (X = Cl, Br, or I) at 0.03—0.02M-OH " concentrations shows deviations from first-order plots early in the reaction the rate data fit a combination of two exponential decays, thought to be competing Sis,2cb and Sn2 processes. The kinetics of aquation of [Ru(NH3)5Cl]Cl2 and m-[RuCl2(en)2]CI,-H2O in mixed water-organic solvent media indicate processes. Hg catalyses the aquation of the former complex [(NH3)5Ru—Cl—Hg]" is formed in a preequilibrium and dissociates to form HgCl. [Ru(phen)3] and [Ru(bipy)3] oxidize cyclohexanone in IM-H2SO4 by outer-sphere processes. In 0.1M-OH with excess RCHO (R = Me or Ph), [Ru(NH3)g] is rapidly converted into [(NH3)5Ru(NCR)]. In basic conditions, the cation reacts with oxygen to form [Ru(NH3)sNO] in the presence of [Ru(NH3)5 NO] is still formed,... 

The recent extension of these thermodynamic models to include the kinetics and mechanisms of organo-metallic interactions has made it possible (1) to quantify the electrochemical availability of these metal complexes to voltammetric systems (Whitfield and Turner, 1980) (2) to examine diffusion and dissociation models for the tremsport of chelated iron to biological cells (Jackson and Morgan, 1978) and (3) to estimate the significance of adsorptive and convective removal processes on the equilibrium specia-tion of metals in natural waters (Lehrman and Childs, 1973). Thus both equOibrium and dynamic models have become an indispensable tool in the identification of the important chemical forms and critical reaction pathways of interactive elements in aquatic environments. 

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